Scientific Alliance Newsletter

Much of northwest Europe is having an unusually cold start to winter (another deadly one - fourth in a row). Admittedly, the British transport network tends to crumble at the first hint of snow, but our near continental neighbours have also suffered disruption. In the meantime, Iceland and Greenland have enjoyed relatively mild weather, so we cannot simply conclude that the northern hemisphere winter is cold and that this therefore puts in doubt the generally-accepted global warming trend. Supporters of the enhanced greenhouse hypothesis rightly argue that it is the longer-term pattern which is important, not short-term weather patterns, however unusual.

The distinction between weather and climate is important. Records for temperature, rainfall, windspeed or whatever are broken somewhere in the world on an almost daily basis. Some maximum and minimum temperature records have stood for many years because they were caused by an atypical coincidence of factors. They tell us nothing about climate unless there is a definite trend over an extended period of time.

Climate itself is not amenable to a simple definition, although it is normally taken to mean the range of typical seasonal weather patterns over a 30 year period. Earlier Springs, for example, can be seen as a sign of a shift in the climate, if such a pattern is consistent over many years. The occasional heatwave or localised flood, on the other hand, are just weather. Shifting jetstream patterns, which have a strong influence on weather patterns in western Europe are one important component of a weather system, but only represent a change in climate if there is an apparently permanent shift north or south.

These distinctions do not, of course, stop the natural human tendency to ascribe a significance to unusual weather patterns which fits their own viewpoint. So, some sceptics will gleefully point to the present cold snap (and even more gleefully at the snow which fell while the UK parliament was voting on the Climate Change bill) as evidence that the IPCC interpretation of climate is wrong. These same people, on the other hand, would dismiss the 2003 heatwave across western Europe (with well-publicised increases in the numbers of elderly people dying in France) as extreme weather caused by a blocked area of high pressure.

On the other hand, for those who subscribe to the mainstream view on the human influence on climate, the interpretation would be reversed. The cold start to winter (following as it does last year’s severe one) is part of the normal variability to be expected. And while most people are careful not to blame global warming for individual weather events, guilt by association is the common position. Thus, 2003 was used by many as an example of what could become the norm in years to come. Meanwhile, there will always be someone prepared to make a link between hurricanes or an unusual monsoon season (with this year’s floods in Pakistan being a case in point) and a warming world.

The distinction between weather and climate is extremely important. Is the Scottish skiing industry just seeing a couple of freak years of good snowfall before it continues a long-term decline, or will a change to colder weather make it a reliable source of income over coming decades? And will those who have invested in English vineyards see a favourable shift in climate which makes them more competitive with continental neighbours or will the English wine industry sink back into obscurity this century?

In truth, no-one knows, although everyone has an opinion. The thousands of negotiators in Cancun are all of the belief that there is a long-term trend towards a warmer world and that the primary driver of that is human activity. With this as a starting point, the goal of most delegates remains to agree a binding commitment to drastic reduction of greenhouse gas emissions over the next few decades. It is accepted that this will not be achieved this year and almost certainly not in 2011, but the strategy remains the same.

Tactically, however, things are very different in Cancun than in the lead-up to Copenhagen. Then, there was still some hope that at least the basics of a post-2012 policy could be agreed. Now, the main aim is to keep the talks alive and relevant for the next couple of years. Once lost, the momentum created over many years would be all but impossible to revive. Inevitably, with so much political and scientific capital invested in the UNFCCC process, many participants are using all the tools available to them to keep the juggernaut rolling forward.

Climate activists and some scientists point to the dangers inherent in a world where average temperatures are 4C or more higher. The latest issue of the Philosophical Transactions of the Royal Society has the theme ‘Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications’. Keepers of temperature series, including NASA and the UK Meteorological Service, are talking up the likelihood of 2010 being one of the three warmest on record (despite there being two months’ worth of data yet to be included). Some small island states continue to insist that rising sea levels will see their demise, despite evidence that coral atolls have remained just above sea level as water levels have risen steadily over thousands of years.

Clearly the last thing that any of the many vested interests want is for the debate about the scientific evidence and its interpretation to be opened up. If the basic science is regarded as settled, the difficult process of agreeing a mitigation policy has a chance of success. If not, the logical way forward is to take whatever emissions reduction steps which make economic sense anyway (in particular, increasing energy efficiency) while concentrating on effective adaptation in areas which are vulnerable (flood defences, water storage and drought-tolerant crops, for example). And as for the move away from fossil fuels, this will inevitably happen during the 21st Century as extraction becomes more difficult, prices rise and viable alternatives are developed. This makes more sense than betting now on wind and solar power to fulfil a large part of our energy needs, at least with the current state of development.

A lot is at stake for all of us, and the distinction between weather and climate is crucial to this. Given the present impasse in negotiating a post-Kyoto deal, practical policymakers should surely be focussing more on adaptive strategies. The distinction between weather and climate can only be made with hindsight.